1. Field of the Invention
The present invention relates to air assist fuel injectors and, more particularly, to the armatures of such air assist fuel injectors.
2. Description of the Related Art
Conventional fuel injectors are configured to deliver a quantity of fuel to a combustion cylinder of an engine. To increase combustion efficiency and decrease pollutants, it is desirable to atomize the delivered fuel. Generally speaking, atomization of fuel can be achieved by supplying high pressure fuel to conventional fuel injectors, or atomizing low pressure fuel with pressurized gas, i.e., xe2x80x9cair assist fuel injection.xe2x80x9d
FIGS. 1 and 2 illustrate a conventional air assist fuel injector 50. The conventional air assist fuel injector 50 receives a metered quantity of low pressure fuel from a conventional fuel injector (not illustrated) and pressurized air from an air/fuel rail (not illustrated). The air assist fuel injector 50 atomizes the low pressure fuel with the pressurized air and conveys the air and fuel mixture to the combustion chamber of an engine.
The pressurized air from the air/fuel rail and the metered quantity of fuel from the conventional fuel injector enter the air assist fuel injector 50 through a cap 52, which delivers the fuel and air to a throughhole of an armature 54. Thereafter, the fuel and air travel through a passageway of a poppet 56, and exit the poppet through small slots near the end or head of the poppet. The poppet 56 is attached to the armature 54, which is actuated by energizing a solenoid 58. When the solenoid 58 is energized, the armature 54 will overcome the force of a spring 60 and move toward a leg 62. Because the poppet 56 is attached to the armature 54, the head of the poppet will lift off a seat 64 when the armature is actuated so that a metered quantity of atomized fuel is delivered to the combustion chamber of an engine.
As illustrated in FIG. 2, the throughhole of the armature 54 is enlarged at the end of the armature 54 facing the cap 52. This enlarged cylindrical volume receives a protrusion from the cap 52 and serves to pass the liquid fuel and air to the passageway of the poppet 56. As further illustrated in FIG. 2, it was conventionally thought to minimize the air volume between the armature 54 and the cap 52. However, this conventional construction often causes liquid fuel to accumulate between the cap 52 and the armature 54, which, in turn, causes poor transient response time between different fueling rates.
For example, if the air assist fuel injector 50 were installed in the engine of an automobile or motorcycle and the operator of the vehicle let off the throttle to slow down the vehicle, the amount of fuel supplied to the air assist fuel injector 50 would decrease. Ideally, the flow rate of fuel exiting the air assist fuel injector 50 would instantaneously decrease when the flow rate of fuel supplied to the air assist fuel injector decreases. However, as described above, liquid fuel tends to accumulate in the area between the cap 52 and the armature 54; it takes time for the air flowing through the air assist fuel injector 50 to scavenge this accumulated fuel out of the injector. At steady fueling rates, this accumulated fuel generally does not create problems. However, this accumulated fuel is delivered from the air assist fuel injector when changing fueling rates and thus adversely affects the amount of delivered fuel when the operator lets off the throttle. This effect essentially delays the response time between the different fueling rates, and decreases the reliability and overall performance of the conventional air assist fuel injector 50.
A further problem associated with other conventional air assist fuel injectors concerns the amount of time it takes the poppet to close, i.e., abut the seat, after the solenoid has been de-energized at high fueling levels. This problem is thought to be caused by surface adhesion and hydraulic delay due to pressure differentials. When increasing the fueling rate supplied to such conventional air assist fuel injectors, the pressure in the volume between the armature and the leg may have a lower pressure than volumes upstream of the armature and downstream of the leg because the pressure is not easily relieved past the bearing for the armature. This pressure differential is most prevalent in the spring pocket when the armature abuts the leg during increasing fueling rates. Because the pressure in the volume between the armature and the leg is not equal with the pressure of volumes upstream of the armature or downstream of the leg at high fueling rates, the spring must overcome a pressure differential that tends to keep the armature in its actuated position and thus keeps the poppet open when the solenoid is de-energized. This effect erratically delays the closure of the poppet at high fueling rates and is termed xe2x80x9chydraulic delay.xe2x80x9d Surface adhesion, i.e., xe2x80x9cstictionxe2x80x9d between the abutting armature and leg also contributes to this erratic closing behavior.
Hence, besides suffering from poor transient response time between different fueling rates, conventional air assist fuel injectors also suffer from erratic closing behavior due to hydraulic delay and surface adhesion at high fueling levels, which further decreases the reliability and performance of conventional air assist fuel injectors.
In light of the previously described problems associated with conventional air assist fuel injectors, one object of one embodiment of the present invention is to decrease the likelihood that fuel will accumulate in the air assist fuel injector and adversely affect transient response times between different fueling levels. A further object of one embodiment of the present invention is to decrease the likelihood that the air assist fuel injector will close erratically due to hydraulic delay and/or stiction.
Other objects, advantages and features associated with the embodiments of the present invention will become more readily apparent to those skilled in the art from the following detailed description. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious aspects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not limitative.